EXPLORATION: Trends and Developments In 2001
Reports of company mergers continued as geophysical survey contractors and instrumentation companies consolidated amid decreased exploration expenditures worldwide. However, in spite of this decline, estimated budgets of over US$2.2 billion were allocated to mineral exploration in 2001. Internationally, many thousands of kilometres of airborne surveys were flown, and new innovative technology emerged even in these rough times.
Many geophysical companies that have exclusively supported the mining industry for years, have also had to turn to other applications for sources of income. Much of the new geophysical equipment and methodologies are applicable to surveys related to archeological applications, unexploded ordinance, potable water, landfill delineation, ground water contamination and problems like acid mine drainage. In this era of heightened awareness of terrorism, geophysical expertise in the detection of hidden orebodies using magnetic, electromagnetic, radiometric, radar and other mineral exploration technologies will also be valued for the detection of a whole new range of concealed objects.
Both Aero Surveys Inc. and EDCON Aero Surveys Inc (EASI) of Denver, Col., reported that the last six months of 2001 has probably been its busiest time in several years. In January 2002, AeroSurveys moved to new offices in Uxbridge, Ont.
Fugro Airborne Surveys (FAS) continued to expand its worldwide operations, in Canada purchasing the assets of Spectra Exploration Geosciences (Calgary, Alta.), Scintrex Surveys (Airborne Division, Toronto), and SIAL Geosciences (Montreal). In Australia, airborne contractor Tesla Airborne Geoscience was acquired, along with Tesla 10. The acquisition in June of Kevron Pty. Ltd. (Perth, Australia) added airborne contractors Kevron Geophysics and subsidiary Geo Instruments. In the United Kingdom, FAS also acquired Robertson Research. Regional offices are now located in Canada (Ottawa and Toronto), Europe (Guildford, U.K.), South America (Santiago, Chile), Africa (Johannesburg), and Australia (Perth) with over 50 fixed-wing aircraft plus leased helicopters.
Sander Geophysics Ltd. (SGL), based in Ottawa, is now the second largest airborne survey company in the world, and after 40 years remains an independent, employee-owned business. SGL specializes in high resolution airborne gravimetric, magnetic and radiometric surveys using fixed-wing aircraft and helicopters. In 2001, the company purchased a fifth turbine-powered Cessna 208B Grand Caravan, increasing SGL’s fleet to seven modern aircraft.
In April, Scintrex Ltd. (Concord, Ont.) combined with LaCoste & Romberg (Austin, Tex.) and Micro-g (Erie, Col.) to form a new company: LaCoste & Romberg – Scintrex Inc. The new company with head office located in Concord, owns both LaCoste & Romberg and Scintrex, and these two will continue as distinct companies with their own separate line of instrumentation. Micro-g retains its name as a division of L&R-Scintrex Inc., which is now the world leader in gravity technology, with the CG-3 Autograv gravity meter, the LaCoste & Romberg G meter, the Gravitron EG meter, Borehole gravity meters and the Micro-g line of absolute gravity meters.
Airborne Geophysical Surveying
Aero Surveys is currently flying HRAM surveys in Libya, in partnership with SCANAIR of France. The large project for several oil company clients, using a Cessna 404 Titan aircraft, is expected to carry on well into the new year. EASI has been in Colombia since mid-summer 2001 flying aerogravity/magnetics and HRAM surveys for several oil companies. The company is also flying a horizontal gradient survey in Colorado.
FAS was again involved in diamond exploration in Canada, with the helicopter division acquiring over 57,000 line-km of data in the NWT. The new higher frequency (101 Khz) available from the DIGHEMVRES proved effective for some kimberlites that were difficult to detect with lower frequencies. FAS also flew resource exploration surveys in Ontario, Quebec, British Columbia, Alberta, Manitoba, the Yukon and parts of Alaska. NASA employed DIGHEM technology to fly a survey in the Haughton-Mars project at Devon Island in the Canadian high Arctic. DIGHEMV systems were also employed in surveys in the United States, Denmark, China, Africa, Australia, several South American countries and Morocco. Major fixed wing surveys flown by FAS included phase three of the Ontario government’s “Operation Treasure Hunt” (OTH) in which 32,000 line-km of GEOTEMTM was flown as well as combined magnetic/radiometric surveys. Ground water surveys in Texas and New Mexico were flown with MEGATEMII, and MEGATEM was used in surveys in Quebec, Ontario and Alberta.
Terraquest Ltd. (Toronto) reported a very active year. One of the highlights was the completion ahead of schedule of the data acquisition portion of a 24,000-line-km high resolution magnetic/gamma-ray spectrometric survey as part of OTH in Ontario. Terraquest claimed another “first”, when a magnetic and radiometric survey was flown in combination with a hyperspectral survey, for a client in the American southwest.
In Airborne Data Acquisition and Processing news, Condor Consulting Inc. (Wheat Ridge, Col.) expanded its suite of AEM processing tools to include the recently released University of British Colombia (UBC) product, ‘EM1dFM’, to process frequency domain helicopter data. EM1dFM can recover both conductivity and magnetic permeability. Condor also expanded its suite of airborne EM case studies for a wide range of deposit types and settings, on their web site.
Developing Technology Inc. (Dev-Tech) of Newmarket, Ont., is producing two new data acquisition systems called AIRLOGS II and AIRLOGS IIB. AIRLOGS II is a Windows-based rack-mount, 24 – 28 VDC data acquisition system, designed to handle multiple sensors, with icon-driven software and full colour graphic displays. AIRLOGS IIB is a miniversion of AIRLOGS II for mag/gradiometer systems only, running on an industrial notebook. Aero Surveys Inc. is now flying with AIRLOGS II, and plans to upgrade completely to this system. Another Dev-Tech development is the Geo-iMAGe Lite colour digital video imaging system, which is aimed at replacing the traditional VCR with digital picture recording. It has sufficient horizontal and vertical overlap (line spacing-dependant) to allow the generation of video pairs and to create a 3D terrain model. Aero Surveys and EASI, which flew Geo-iMAGe in their systems in Colombia and in Libya, reported excellent results.
The latest release of Encom Technology Pty. Ltd. (Sydney, Australia) is ‘Discover V4.0’, a geoscience plug-in for MapInfo Professional. The new Enhanced Layer Control uses a single, hierarchical control that facilitates grouping of layers for simultaneous control, dragging and dropping of layers between groups, and a “true” previous-button that allows stepping back through previous views. The new Extended Grid Handlers enable Discover to support Geosoft, ER Mapper and MapInfo formats for all Discover grid functions. Also released in 2001 was ‘Profile Analyst V3.0’, which now enables 3D visualization of surfaces and sections and ‘fly-through’ of conductivity-depth sections along with full 3D rotation, zoom and pan.
FAS is consolidating (under the name of ATLAS) the unique and the best elements from the various software and processing techniques developed by each of the firms that now make up Fugro Airborne Surveys. In new hardware, FAS is now offering the ARGUSTM airborne hyperspectral reflectance profiler that measures reflectance over approximately 200 spectral channels in the wavelength range 500 to 2,500 nm (VNIR and SWIR) and 8,000 to 13,000 nm (TIR). It operates in a spectral range that has the best reflectance for indicator minerals marking alteration or key “tracer” minerals associated with mineralization.
IGM Ltd. in the United Kingdom has just released version 5.1.1 of GeoExpress, an advanced 3D integration and visualization program for geoscientific, spatial data. Ease of use is facilitated by i
ts ability to read formats from other exploration software companies like Geosoft, ERMapper, Encom and UBC’s inversion modeling consortium, combined with its customizable interface. In 2001, the company entered into an agreement to become a Geosoft Plus Partner and to deliver an integrated and simplified 3D grid viewer for Oasis Montaj, the industry’s de facto leading environment for working with spatial data.
SGL reported the company has implemented a new method that removes radon effects from 256-channel airborne gamma-ray spectrometer data without using upward-looking detectors.
Terraquest claims to be the first airborne survey company in North America to include high-resolution colour digital video camera flight path recovery. Using the ‘Geo-iMAGe Lite’ colour digital imaging system from DEV-TECH, high-resolution video images can be acquired and recorded in a format that can be read on any standard PC. These images, combined with GPS position, time, height above ground, height above sea level, pitch and roll axis tilt, make it possible to generate digital 3D terrain models that can be integrated into the geophysical data set.
Other new developments at Terraquest include the installation of wing tip pods on the company’s Navajo to make a second horizontal gradiometer system, and a planned new tail stinger to be installed on its Cessna 206 equipped with a horizontal gradient system. The stinger will incorporate a new two-frequency electromagnetic system that has been in development for over a year. Ground tests of the new EM system have exceeded expectations.
In Aeromagnetic Surveying, the helicopter systems from FAS now include 3D-GMTM, a 3D gradient magnetics system consisting of three Scintrex CS-2 cesium vapour magnetometers mounted with a separation of 3 m in all directions, in a towed bird. The along-line sample interval is 2.5 m.
Goldak Exploration (Saskatoon, Sask.) is now operating two Piper Navajo magnetic survey aircraft in a three-axis (four mag) magnetic gradient configuration, which they call the “Tri-Maxial” system. They believe it is the only ‘true’ three-axis gradient system in North America. Each platform consists of four Geometrics 822A cesium vapour magnetometers, two mounted on wingtips and two vertically separated on the tail stinger. The sensor separation on the tail stinger is believed to be the largest in the industry and has the highest possible signal-to-noise ratio. Approximately 250,000 line-km was flown with the gradiometer in the last year. Goldak is also beginning to use an array of GPS antennae on the aircraft to determine continuous 3D gradiometer attitude in post-processing to remove the effects of pitch, roll, yaw and wind crab.
In 2001, SGL installed and tested tri-axial magnetic gradiometer systems on three of its Cessna Grand Caravans. Besides performing surveys for several industrial clients, the company completed large aeromagnetic surveys in Greenland for the Greenland Bureau of Minerals & Petroleum, and in the Canadian Arctic for the GSC. A very large airborne magnetic gradiometer survey is underway in Saudi Arabia using two of SGL’s Cessna Grand Caravans outfitted with tri-axial magnetic gradiometer systems.
Scintrex introduced its new CS-3 high sensitivity cesium magnetometer sensor which includes automatic hemisphere switching, among other improvements, while still retaining the best features of the predecessor CS-2.
Recent advances in Airborne Electro- magnetic technology include development by FAS of the fixed wing MEGATEMII which now has a dipole moment effectively twice that of MEGATEM. The CASA-mounted GEOTEMTM time domain airborne EM system was also upgraded to the new GEOTEM1000 with a significantly increased transmitter dipole moment, equivalent to that for the original MEGATEMTM at the lower frequencies of 30 and 15 Hz.
FAS has advanced helicopter resistivity mapping techniques, building on the DIGHEMV and DIGHEMVRES technology of an all-coplanar five-frequency system with frequencies from 400 Hz to over 100 kHz. The new DIGHEMV-DSP version offers the advantages of a fully digital EM system, including automated airborne calibration, minimal drift, lower noise and real-time signal processing. The new DIGHEMRESOLVE is a digital six-frequency helicopter system with combined coplanar and coaxial coil pairs, the incorporation of internal calibration coils and all of the features of the above systems. In 2001 the first production survey was flown for the United States Geological Survey (USGS) in Florida.
In Airborne Gravity Developments, several airborne gravity surveys were flown by SGL for oil industry clients, using its Airborne Inertially Referenced Gravimeter (AIRGrav) system. Surveys flown in North and South America included drape surfaces in the Rocky Mountains with over 1,200 m of vertical change. In addition, the company flew the first mineral exploration survey using AIRGrav, which delineated previously unmapped drill targets.
Ground Survey Techniques
Mira Geoscience Ltd. (Montreal) has worked with Mirarco in Sudbury to introduce a new ‘visualarium’ driven by GOCAD software. Mirarco (Mining Innovation Rehabilitation and Applied Research Corp.) is a non-profit company founded in 1998 through collaboration between Laurentian University in Sudbury, and both the public and private sectors of the mining industry. The new Virtual Reality Lab (VRL), which opened in September, is a 3D immersive environment in which you can sit inside 3D models to interpret complex data and solve problems in ways limited only by the imagination.
In Data Processing and Positioning news, Geonics Ltd. (Mississauga, Ont.) introduced several new Windows-based software programs for its line of ground conductivity meters as well as for its EM61 and EM63 metal detectors. Lamontagne Geophysics Ltd. (Kingston, Ont.) has further developed its EM modeling software MultiLoop 3, for thin conductors. The speed of the computation-intensive part of the code has been increased by a factor of more than 40 over the early 2001 prototype. It can model multiple curved conductors with varying conductance using high resolution tri-mesh gridding. In early 2002, a beta version will be available with an initial feature set that includes multiple meshed conductors, waveform/sampling menus, and curved borehole trajectories.
Quantec Geoscience Ltd. (Porcupine, Ont.) introduced ‘3DQuest’, a four-phase exploration process consisting of: 1. Common Earth Modeling (using GOCAD, available from Mira Geoscience, a division of Quantec); 2. conversion of the geologic models to physical property models using calibrated borehole geophysical logs; 3. ground geophysics using the new “TITAN 24” – MT/IP, a deep electrical earth imaging survey system capable of an average of 2.5 km per day of continuous AMT/MT/IP; and 4. data processing, carried out at two new 16-node pentium-4 cluster processing centres in Toronto, and Reno, Nev., using proprietary inversion programs that include 2D MT, DC Resistivity/IP and joint DC/MT and 3D DC Resistivity/IP.
In Borehole Geophysics, Icefield Tools Corp. (Whitehorse, Yukon) continued development of its line of MI3 electronic borehole deviation tools. The MI3 tools now come with a full suite of software for DOS, Windows and the PalmPilot. The standard tool diameter is now 25.4 mm, which permits surveying through-the-bit with AQ wireline systems to a depth of 650 m. A 33.4-mm diameter tool with a pressure-depth rating of 3,500 m is also available.
Mount Sopris Instrument Co. Inc. (Golden, Col.) completed development of a new 38-mm diameter spectral gamma logging tool. The temperature-compensated downhole digital probe can transmit either a 512- or a 1,024-channel spectrum. Processing software allows for: spectral calibrations based on temperature, time- or depth-based stacking, outputting logs from user-specified channels, spectral stripping of K, U and Th and performance of spectral fitting with user-defined library spectra.
In the United Kingdom, Robertson Geologging Ltd. (Deganwy) has developed a new sonar cavity s
canner. The probe uses a low-frequency rotating ultrasonic transmitter/receiver head to image water-filled voids up to 150 m in diameter. Data are acquired as a series of horizontal cross-sections at successive depth stations. These are reconstructed by the operating software to produce a 3D oriented image of the cavity.
In Ground Electromagnetic developments, Geonics reported an improvement by an order of magnitude in the signal-to-noise ratio of its EM63 full-time high power metal detector. This results from addition of a noise compensation coil and improvements in signal processing software. The company also introduced an underwater version of its EM61-MK2 high sensitivity metal detector.
Lamontagne Geophysics reported its new UTEM 4 high performance large loop electromagnetic transmitter includes a completely digital current regulation control system. It also has a new time control system allowing changes of base frequency without resynchronisation, and (in conjunction with the receiver) adaptable pre-emphasis/deconvolution filters for optimum noise reduction over a range of base frequencies from 0.5 Hz to 100 Hz. Compared to the UTEM 3 transmitter, the maximum peak-to-peak output voltage increased from 440 V to 1,000 V, peak-to-peak current increased from 12 A to 18 A, and the output voltage slew rate increased from 8 million V/s to 70 million V/s. Full-scale field trials of the prototype unit were scheduled for early 2002.
In Ground Magnetic Surveying, Scintrex introduced the ‘SMARTMAG SM-4G Special’ specifically designed for very highly sensitive magnetometry in archeological applications. The company reports that the SM-4G is becoming more widely used in the field of archeological geophysics as well as in metal detection.
Magnetotelluric and Induced Polarization Developments saw Quantec introduce the “TITAN 24” – MT/IP, a 24-bit distributed acquisition survey (DAS) system capable of deep electrical earth imaging. Four Titan systems are available, with two of these in Canada. Multiple configuration IP surveys are run simultaneously (capable of N= 1 to 36 or greater). Titan DAS systems can map lithology, structure, alteration and mineralization to below 1,000-m depth.
In Ground-Penetrating Radar (GPR) news, the new Rock Noggin from Sensors & Software Inc. (Mississauga) is a small hand-held GPR unit designed to image into rock, but it can also be used on soils and other materials. It is a self-contained, battery-powered unit that comes complete with acquisition and display software. Based on ground-penetrating radar principles, the Rock Noggin sends out a weak radio wave signal that bounces off internal structure in the rock. The echoes are recorded and displayed on the screen. It is suitable for locating fracture zones, localized mineralization, crystals, voids and changes in rock types.
Ground Radiometric Surveying Dev- elopments saw Geofyzika a.s. (Brno, Czech Republic) announce two new gamma-ray spectrometers. The GS-512 is designed for 512-channel operation in field and laboratory use. The unit is equipped with an LCD screen to display measured/calculated data and full gamma ray spectra at one spectrum per second. The assay mode yields data in % K, ppm eU and ppm eTh. Up to eight ROI’s (regions of interest) can be set by the user. Also included are: an RS-232C interface for an optional GPS unit, a range of NaI(Tl) detector sizes from 2 x 2-inch to 4 x 4-inch or a laboratory detector with a low-background lead shield and processing software. The MGS-150 is a newly designed compact 256-channel gamma-ray spectrometer for field evaluation of K, eU, eTh contents using an internal 2 x 2-inch NaI (Tl) detector, with a larger external detector optional. The unit also has an LCD screen, assay mode and up to eight ROI’s.
GF Instruments, s.r.o. (Brno, Czech Republic) introduced the DCS-1, an automatic (PC-controlled) laboratory drill core scanner for precise continuous gamma-ray and magnetic susceptibility measurements of drill core samples. The gamma-ray unit is a 512-channel spectrometer with a NaI(Tl) 3 x 3-inch detector that provides quantitative K, eU, and eTh concentrations. Magnetic susceptibility is measured with a sensitivity of 1×10-5 SI units.
SGL designed and built a new ground-based survey system for extremely high sensitivity environmental monitoring of nuclear sites. The system includes four 16.8-litre gamma-ray detectors mounted on a specialized trailer that can be towed behind a small tractor. Data-recording and GPS navigation are performed by the company’s standard NAVDAS data acquisition and navigation computer. Using this system SGL and Gamma-Bob Inc. (Gloucester, Ont.) were able to successfully locate particle sized 60Co sources buried below gravel and embedded in asphalt at a nuclear generating site.
Resistivity Surveying Advances in 2001 include the new RS-100D from Geofyzika, which is a compact portable DC resistivity unit capable of operation with up to 512 electrodes primarily for resistivity imaging, profiling and SP measurements. The unit consists of a 100-W transmitter, four-channel receiver and a powerful embedded computer with extremely low power consumption.
Geometrics Inc. (San Jose, Calif.) released the OhmMapper TR2, a two-receiver version of the TR1. The OhmMapper resistivity meter couples current into the ground via the capacitance of a set of coaxial cables so that there are no electrodes to insert into the ground. With the TR2, two resistivity measurements at two different n-spaces, are made simultaneously to speed up data collection for a 2D or 3D resistivity survey.
The new MRS-256 micro-resistivity system by GF Instruments was designed for detailed studies of resistivity and self potentials of the earth and artificial objects. The unit consists of a transmitter (0-560V/ to 1 A), receiver (24-bit, input impedance 10 GO), power supply and multi-electrode system controlled from a PC notebook. The data are processed with a back-projection method designed at the University of Palermo, which results in detailed 3D models and 2D sections for surveys of shallow structures.
Premier Geophysics Inc. (Langley, B.C.), which provides consulting and contracting services in 3D earth resistivity mapping, offers its Multiple Total Field 3D resistivity system (MTF 3D), also known as E-SCAN. It is part of a planning, data acquisition and 3D interpretation package to assess deep geo-electric signatures from the conductive to the resistive end of the electrical spectrum.
The field setup–typically comprising over 130 microprocessors, hundreds of electrodes and up to 100 km of wire–was initially developed in 1976-1982 for geothermal exploration of extreme terrain conditions, from R&D supported by the GSC and BC Hydro & Power Authority. The technology is based on a dense, multi-directional 3D raw data set acquired by the deployment of an unlimited number of grid electrodes to facilitate the mapping of the entire DC electric potential field, as current is injected at each of the hundreds of grid points in turn. The company claims that today’s modern 3D inversion software can take the 3D raw data set to generate subtly-resolved, terrain-proof imagery including the seldom-used resistive end of the conductive-resistive spectrum. In 2001, MTF 3D was used in Nevada and in Saskatchewan’s Athabasca Basin.
Patrick G. Killeen, Ph.D., is an emeritus scientist at the Geological Survey of Canada, Ottawa